Objective. The study was done to estimate the incidence of malnutrition in children under 5 years old in Tu Ky district, Hai Duong Province in 2023. Subjects and Method. Subjects included 602 children under 5 years old in the study setting. The method was a cross-sectional study. Results. The incidence of underweight was 6.1%, stunting was 12.3%, and wasting was 10.8%. Underweight affected more females than males (6.4% so vs 5.9%), similarly, wasting affected more females than males (11.0% vs 10.6%). In contrast, stunting affected more males than females (14.2% vs 10.4%). The incidence of 3 kinds of malnutrition gradually increased and peaked when children were 2 to 3 years old, then the incidences gradually decreased when children were 4 to 5 years old. Conclusions. Malnutrition is a common disease in children under 5 years old in Tu Ky. The disease occurs in both males and females but is moderately common.